Of the several builds I've tested, this one was by far the smoothest. Ganyu is played as sub dps with Elegy; combined with Diona's Sac Bow the energy regeneration is fairly good. While someone like Ayaka (who I don't have) will surely provide more damage, I find Chongyun to be extremely valuable for his extra aoe damage and cooldown reduction.
Shenhe's build is shown at the end of the video; I plan to replace the hat with an atk% one. I have a few artifacts to level up that will hopefully give her some extra ER%.
Chongyun is lvl 79/80 with low level talents, Diona is only lvl 70. For such a low investment team I was really surprised by how well it all fits together. Ganyu could very easily be replaced with Rosaria for a more budget option.